Lowe G, Tansley G
Eur J Biochem. 1984 Feb 1;138(3):597-602. doi: 10.1111/j.1432-1033.1984.tb07956.x.
Adenosine (S)-5'-[alpha-17O, 18O2]triphosphate has been synthesized and used to investigate the stereochemical course of activation of tryptophan by tryptophanyl-tRNA synthetase from beef pancreas. It is shown that the reaction proceeds by displacement of Mg pyrophosphate from MgATP with inversion of configuration at P alpha. Tryptophanyl-tRNA synthetase catalyses positional isotope exchange in adenosine 5'-[beta-18O2]triphosphate in the presence of tryptophan but not in its absence or in the presence of the competitive inhibitors tryptamine and tryptophanol. These observations eliminate a multi-adenylyl transfer or dissociative mechanism and in combination with the sterochemical study leave a direct associative 'in line' displacement at P alpha of MgATP as the only tenable mechanism for the activation of tryptophan by tryptophanyl-tRNA synthetase.
已合成腺苷（S）-5'-[α-17O，18O2]三磷酸，并用于研究来自牛胰腺的色氨酰-tRNA合成酶激活色氨酸的立体化学过程。结果表明，该反应通过从MgATP中取代焦磷酸镁进行，Pα构型发生反转。色氨酰-tRNA合成酶在色氨酸存在下催化腺苷5'-[β-18O2]三磷酸中的位置同位素交换，但在色氨酸不存在或存在竞争性抑制剂色胺和色醇时则不催化。这些观察结果排除了多腺苷酰转移或解离机制，并且与立体化学研究相结合，使得MgATP的Pα处直接缔合的“直线型”取代成为色氨酰-tRNA合成酶激活色氨酸的唯一合理机制。
